Chronic pain may have multiple causes including inflammation, peripheral nerve injury, cancer, AIDS, and diabetes. Treatment of chronic pain has included the administration of analgesics.
Analgesic compounds are agents which alleviate pain without causing a loss of consciousness; they may also reduce inflammation. Known analgesics have not been particularly effective in the treatment of chronic pain. For instance, aspirin derivatives and non-steroidal anti-inflammatory agents have limited efficacy and have a number of side-effects including interference with blood coagulation and the exacerbation of peptic ulcers; morphine and opioid analgesics have shown some beneficial effects, but cause side-effects such as marked tolerance, and addiction and withdrawal syndromes; and the known N-methyl-D-aspartate (NMDA) receptor antagonists are effective in certain animal models, but produce behavioural side-effects including motor impairment, learning impairment, and ataxia.
U.S. Pat. No. 5,656,267 (Aug. 12, 1997) describes a method of alleviating chronic pain involving the transplantation of cells into a region of the central nervous system of patients suffering from chronic pain. However, this method is not practical.